This application is the national phase of international application PCT/SE98/01853 filed Oct. 15, 1998 which designated the U.S.
This invention relates to a process for producing a wood material which possesses controllable bending properties. The process can be used to produce a wood material which possesses a high degree-of elasticity and a high degree of bending ability. The resulting wood material can be readily deformed into a desired shape, after which it is also possible to lock this shape in a simple manner, such that the wood material regains normal bending properties, while the shape has been permanently altered. The invention also relates to a wood material which has been produced using the above mentioned process.
Constructions and objects of bent wood have been used by man since time immemorial. Since wood is a rigid material, it has to be softened before being shaped and bent so that it does not split. Traditionally, this softening has been achieved using heat, or, alternatively, using a combination of heat and moisture (for example using steam). Wood has also been softened by impregnating it with chemicals such as ammonia, polyethylene glycol and pyridine.
In modern times, alternative wood materials which possess a high degree of bending and shaping flexibility have also been developed. One type of process is based on thin discs of wood being glued to form a laminated structure whose plasticity is greater than that of the raw wood material. Examples of this are described in JP, A, 9/70804 and JP, A, 7/246605. However, the flexibility of the material described in these documents is not entirely satisfactory, either. Heat is required in connection with the bending step. Finally, the wood material is unable to recover its normal rigidity after the desired deformation has taken place. There is therefore a need for improved processes for temporarily increasing the elasticity of wood materials and for decreasing this elasticity to the normal level once again after the desired bending has taken place.
It has now been found that it is possible greatly to increase the elasticity and bendability of diffuse-porous wood by means of a process which comprises the following steps:
a) supplying a specimen of diffuse-porous wood; and
b) isostatically pressing the specimen in a) with a pressure of at least 500 bar.
The rigidity is increased once again by immersing the wood specimen in a liquid for a period which is sufficiently long for the liquid to be able to penetrate into the whole of the wood specimen and then drying the specimen.
Definitions:
The term xe2x80x9cisostatic pressingxe2x80x9d which is used here relates to pressing with a pressure which is equally great in all directions in space. Pressing wood with a pressure of this nature is described in WO 95/13908. xe2x80x9cDiffuse-porous woodxe2x80x9d is wood in which the vessels are evenly distributed and are of approximately uniform size over the whole of the annual ring. Examples of trees having diffuse-porous wood are alder, aspen, birch, beech, maple, eucalyptus, Canadian sugar maple, Betula pendula, Acer pseudoplantanus, Acer rubrum, Nyssa sylvatica, Liquidambar styraciflua, Popolus balsamifera, Fagus sylvatica, Banksia prionotes and Banksia ilicifolia.
The term xe2x80x9cwood specimenxe2x80x9d is used here to signify a specimen of diffuse-porous wood. A xe2x80x9ccomposite wood specimenxe2x80x9d refers to a specimen which consists of several smaller diffuse-porous wood specimens which have been glued together parallel to the direction of the fibres in the constituent specimens. In principle, most types of glue which are suitable for wood can be used when producing composite wood specimens. Examples which may be mentioned are cold-water glue, hot-melt glue, solvent-based glue, emulsion-based glue and polymerization-based glue having one or two components. Use can be made, in particular, of glue which contains polyvinyl acetate emulsions, PVC, polystyrene, urea, melamine, melamine-formnaldehyde, phenol and polyurethane. It is simple for a skilled person to select a suitable glue type on the basis of the given conditions.
The term xe2x80x9cliquidxe2x80x9d is used here to signify a liquid which is able to penetrate into diffuse-porous wood. Examples of such liquids are water and linseed oil/turpentine in a ratio by weight of 1/100-100/1. The liquid can also contain other substances such as dyes and substances which increase resistance to rotting and fire.